Oscillation suppression circuitry

ABSTRACT

An oscillation suppression circuit for use particularly with crossed-field traveling wave tubes used as backward wave oscillators, the preferred embodiment including a tuned circuit, resonant at the frequency to be suppressed, which is coupled to the sole electrode circuit.

United States Patent [72] Inventor Merle R. Boyd [51] Int. Cl 1103b 1/04 Auburndale, Mass. [50] Field of Search 331/82, [2]] Appl. No. 816,300 105; 332/7 5253 3 Primary Examiner-John Kominski Assignee Raytheon p y Attorney Philip J. McFarland Mass.

ABSTRACT: An oscillation suppression circuit for use par- [54] gQE fi E CIRCUITRY ticularly with crossed-field traveling wave tubes used as g backward wave oscillators, the preferred embodiment includ- [52] U.S.Cl 331/82, ing a tuned circuit, resonant at the frequency to be sup- 331/105, 332/7 pressed, which is coupled to the sole electrode circuit.

Z6\\Z\\ 4QR\\\\ W""II""II" NH f 2.9- -29 EC 1 25 |b" "fir-'1 3/ 1 33F J WW/II rlmm 338 IO 37 2| MODULATION SOURCE Patented March 9, 1-971 3 v v\\\\\\ n... M N v 1 m v w 4 8 z K -1. /m. "w 9 ME lmw M 8 fi ,W m 9 v m y w 8 C wf r w m J INVENTOI? MERLE R. BOYD OSCILLATION SUPPRESSION CIRCUITRY BACKGROUND OF THE INVENTION This invention pertains generally to control circuits for traveling wave tubes and specifically to circuits of such type which prevent unwanted oscillations in such tubes.

It is well known in the art that crossed electric and magnetic field traveling wave devices, sometimes hereinafter referred to as traveling wave tubes or TWT, may be arranged to frequency-modulate an oscillatory signal. It is common practice in such cases to connect an alternating source between the cathode and the sole electrode, or sole, of a TWT. In view of the requirement that the sole be negatively biased with respect to the cathode, any such connection must include a direct current path. Consequently, modulating sources are frequently shunt-connected to the sole when frequency-modulation is desired and a choke is inserted as a load in the sole/cathode circuit without adding any appreciable resistance in the sole bias circuit.

It has been found that the characteristics of a TWT and the characteristics of any choke are such that an oscillatory circuit exists, the inductance of the coil combining with interelectrode capacitances of the TWT, the distributed capacitance of the coil and the stray capacitance of associated circuitry, to form a parallel resonant tank circuit. Under certain operating conditions, where the sole exhibits a sufficiently low negative dynamic resistance, self-sustaining oscillations resultwhich, at best, detract from proper tube performance and, at worse, render such performance impossible.

Therefore, it is a primary object of this invention to provide an improved circuit for use in frequency modulating a TWT.

Another object of this invention is to provide an improved circuit which minimizes the chance of undesired oscillations of a TWT without introducing unwanted loading effects.

SUMMARY or THE INVENTION The foregoing and other objects of this invention are attained generally by providing, when frequency-modulation of a TWT is desired, frequency-sensitive circuitry in series connection with the sole bias source of such tube, the so-provided circuitry being arranged so as to permit the proper bias voltage to be applied between the sole electrode and the cathode and also to present a low impedance to unwanted oscillatory signals which ordinarily detract from the desired performance of the TWT and a high impedance to oscillatory signals of all other frequencies.

BRIEF DESCRIPTION OF THE DRAWING For a more complete understanding of this invention reference is now made to the drawing in which the only FIG.

schematically shows the contemplated circuitry in combination with a TWT and a modulating source.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the FIG., it may be seen that the contemplated circuitry 10, described in detail hereinafter, preferably is used in conjunction with a conventional crossed-field traveling wave tube, as TWT 12, and a conventional modulation source 14. v

Thus, TWT 12 which will be here recognized to be operated as a backward wave oscillator, includes, within an evacuated metallic envelope I3 fabricated from a nonmagnetic material, a cathode electrode 15, a control electrode 17, an accelerating electrode 19, a sole electrode 21, a slow wave structure (or With the cathode electrode 15, the control electrode 17, and the accelerating electrode 19 connected, respectively, to bias sources E, E, and E and the slow wave structure 23 connected through a choke 24 to ground, an electron beam is fonned and propagated between the sole electrode 21 and the slow wave structure 23 to the collector electrode 25, passing through the magnetic field (as indicated by the circles 29) and the electric field (not shown) existing between the sole electrode 21 and the slow wave structure 23. The electrons in such beam are, of course, absorbed either by the collector 25 or the slow wave structure 23 in a known manner. The device described is capable of generating, in a known manner, microwave oscillations. The frequency of the oscillation is detennined by the strength of the magnetic field and of the electric field existing between the sole and slow wave structure. Consequently, when the modulation source 14 is energized, the electric fields within the TWT 12 are varied by the output signal of such source to produce a frequency-modu lated signal at terminal 23A.

Unfortunately, the just described circuit is deleteriously affected by interelectrode capacitances, stray capacitances and the distributed capacitance of the primary winding 33? (which will be recognized as being, per se, the equivalent of the usually used choke). These capacitances, represented in FIG. 1 by capacitor 35 (which is shown in phantom in FIG. I), combine with the primary winding 33? to form a parallel resonant circuit. Consequently, under certain conditions of operation (which depend upon Q of the parallel resonant circuit and the sole electrode dynamic resistance) cyclic variations may exist which cause self-sustaining oscillations to occur. These oscillations, being impressed on the sole electrode, modulate the signal at the terminal 23A in an unwanted way. The addition of the remaining elements of the contemplated circuitry 10, now to be described, obviates the occurrence of such selfsustaining oscillations.

The just-referred-to elements include a secondary winding 338, a capacitor 37 and a resistor 39 connected as shown to coact with the primary winding 331. If then the capacitance of capacitor 37 is selected in any convenient manner, it is obvious that the oscillatory circuit formed by such capacitor and the secondary winding 33S may be tuned to the frequency of natural oscillations of the oscillatory circuit formed by the primary winding 33F and the equivalent capacitance indicated by the capacitor 35. When such tuning is accomplished, and disregarding the effect of the resistor 39 for the time being, the maximum resistance is coupled into the primary winding 33P.

Consequently, the resultant Q of the parallel resonant circuit (primary winding 33? and capacitor 35) may be lowered to the value required to suppress unwanted oscillations in the TWT 12.

The resistor 39 represents a means of adjusting the Q of the secondary tuned circuit for optimum performance. It has been found, for example, that a very high Q coupled circuit requires resistive loading (to lower the Q) to broaden the frequency spread of high values of coupled resistance for stability.

While this invention has been described with reference to one particular embodiment, it is evident that other embodiments incorporating its concepts may be used. It is felt, therefore, that this invention should not be restricted to its disclosed embodiment but rather should be limited only by the spirit and scope of the appended claims.

I claim:

1. In combination with a crossed-field backward wave traveling wave amplifier tube having a sole electrode, an oscillation suppression circuit comprising:

a. a transformer having a primary and a secondary winding, the primary winding being serially connected between the sole electrode and the bias source therefor; and,

b. means, connected across the secondary winding, for forming a resonant circuit having a resonant frequency at the same frequency as the frequency of oscillations to be suppressed. v

2. An oscillation suppression circuit as in claim I having additionally, a resistor in circuit with the resonantcircuit for adjusting the Q thereof. 

1. In combination with a crossed-field backward wave traveling wave amplifier tube having a sole electrode, an oscillation suppression circuit comprising: a. a transformer having a primary and a secondary winding, the primary winding being serially connected between the sole electrode and the bias source therefor; and, b. means, connected across the secondary winding, for forming a resonant circuit having a resonant frequency at the same frequency as the frequency of oscillations to be suppressed.
 2. An oscillation suppression circuit as in claim 1 having additionally, a resistor in circuit with the resonant circuit for adjusting the Q thereof. 